The modulation of the immune response by psychosocial stressors has important implications for individuals with chronic illnesses such as human immunodeficiency virus (HIV) or cancer. A number of studies have indicated that stressors have the ability to affect a number of markers of immunocompetence. There is, however, considerable variability both within studies and across studies in the magnitude and nature of these results. Any model of stress which fails to account for these individual differences falls short in describing the stress-immune relationship. One potential factor contributing to this variability may be the early experience of the organism. Herein, we will continue the study of the long term impact of early maternal separation on a number of behavioral, endocrine (cortisol and growth hormone), and immunological (acquired and innate immunity) regulation in socially housed nonhuman primates. Social housing also permits study of the mitigation of both the acute and long term effects of maternal separation by other social factors such as social affiliation. Specifically we will monitor innate (natural cytotoxicity, NK cell number, lL-2 production) and acquired (generation of specific antibodies, antigen stimulation) immunity in 6 month old pigtail and bonnet macaques experiencing a 2 week maternal separation while remaining in their natal social group. Quantified behavioral observations will be collected throughout the study in addition to assessment of plasma levels of cortisol and growth hormone. At fifteen months of age the separated and matched control subjects will be transferred from their natal social group to a follow up group for continued behavioral, endocrinological, and immunological testing during a series of novel social and appetitive challenges between the ages of 15 and 42 months. We expect to observe that species and early experience affects subsequent response to these challenges. As the incidence of HIV rises in younger populations, specifically in teen populations who have experienced significant stressors during their early development, studies such as the present become particularly important.